[01/13] clk: tegra: Add binding for the Tegra124 DFLL clocksource

Commit Message

Tuomas Tynkkynen July 15, 2014, 8:23 p.m. UTC

On 14/07/14 13:22, Mark Brown wrote:
> * PGP Signed by an unknown key
> 
> On Mon, Jul 14, 2014 at 11:24:35AM +0200, Thierry Reding wrote:
>> On Mon, Jul 14, 2014 at 10:12:33AM +0100, Mark Brown wrote:
> 
>>> The selector value is opaque, it's entirely up to the driver to define
>>> it.  If you could tell me what "this" is I might be able to advise on
>>> how to do it.
> 
>> Tegra124 (and later, also some earlier variants) have this DFLL clock
>> that can program a PMIC automatically depending on the CPU frequency.
>> This DT binding did propose putting this into device tree as a table of
>> <frequency value> pairs where the frequency corresponds to the CPU
>> frequency and the value is the register value to be programmed into the
>> PMIC by the DFLL hardware (there are two additional properties to define
>> the slave address and the register offset).
> 
>> Andrew proposed that this table could instead be built by using
>> regulator_list_voltage() instead. However, due to the fact that the DFLL
>> hardware needs to know the immediate value to write into a register, the
>> requirement would be for a 1:1 mapping between selector and register
>> value. Given that the API needs to cover the general case I don't see
>> how it could practically ensure this.
> 
> Well, if you're going to do that you've already created a private API
> between the regulator driver and the device since you're assuming that
> the device is controlled only by register writes to a single register
> bitfield which isn't always the case.
> 
> As with all these things it would also be better to extend the regulator
> API so that users like this can discover the register address and so on
> too rather than having to replicate that information in the device tree.
> No sense in having to specify this information multiple times.
> 

That sounds indeed useful for this case. How'd the following interface
sound for the register offset / selector-to-register-value conversion?
The I2C address would be a bit trickier to get as it would touch the
regmap stuff as well, but perhaps it would be a good idea to have a
phandle to the I2C device itself, and then parse the reg field for
the address.

Comments

Mark Brown July 15, 2014, 10:52 p.m. UTC | #1

On Tue, Jul 15, 2014 at 11:23:39PM +0300, Tuomas Tynkkynen wrote:

> That sounds indeed useful for this case. How'd the following interface
> sound for the register offset / selector-to-register-value conversion?
> The I2C address would be a bit trickier to get as it would touch the
> regmap stuff as well, but perhaps it would be a good idea to have a
> phandle to the I2C device itself, and then parse the reg field for
> the address.

This looks fine, can you submit properly please?  For the I2C address
why not just have an interface to get the regmap and then provide a way
to get the underlying device back from the regmap?

Thierry Reding July 16, 2014, 8:01 a.m. UTC | #2

On Tue, Jul 15, 2014 at 11:52:52PM +0100, Mark Brown wrote:
> On Tue, Jul 15, 2014 at 11:23:39PM +0300, Tuomas Tynkkynen wrote:
> 
> > That sounds indeed useful for this case. How'd the following interface
> > sound for the register offset / selector-to-register-value conversion?
> > The I2C address would be a bit trickier to get as it would touch the
> > regmap stuff as well, but perhaps it would be a good idea to have a
> > phandle to the I2C device itself, and then parse the reg field for
> > the address.
> 
> This looks fine, can you submit properly please?  For the I2C address
> why not just have an interface to get the regmap and then provide a way
> to get the underlying device back from the regmap?

Is it mandatory for regulators to use regmap? Also I'm not sure how this
will work with MFDs, since the device may not be the actual bus device,
but rather a child of the MFD (and what we want access to is the MFD).
Perhaps for regmaps that would work in most cases since MFDs seem to
aften share the regmap with their children. However, the code in
regulator_register() at least indicates that even then it's possible to
have a regmap in children that's different from the top-level MFD.

Thierry

Mark Brown July 16, 2014, 11 a.m. UTC | #3

On Wed, Jul 16, 2014 at 10:01:34AM +0200, Thierry Reding wrote:
> On Tue, Jul 15, 2014 at 11:52:52PM +0100, Mark Brown wrote:

> > This looks fine, can you submit properly please?  For the I2C address
> > why not just have an interface to get the regmap and then provide a way
> > to get the underlying device back from the regmap?

> Is it mandatory for regulators to use regmap? Also I'm not sure how this

No, but this is for a limited subset of devices that the hardware knows
how to write to directly which means that they're restricted to things
that can be supported with regmap (or already know how to interact with
the hardware and don't need this interface at all).  The proposed patch
already relies on regmap - it's passing back the information the regmap
helpers use.

> will work with MFDs, since the device may not be the actual bus device,
> but rather a child of the MFD (and what we want access to is the MFD).

> Perhaps for regmaps that would work in most cases since MFDs seem to
> aften share the regmap with their children. However, the code in
> regulator_register() at least indicates that even then it's possible to
> have a regmap in children that's different from the top-level MFD.

Right, drivers can say exactly which regmap to use.

Patch

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index c563d93..a5efb96 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2228,6 +2228,63 @@  int regulator_list_voltage(struct regulator *regulator, unsigned selector)
 EXPORT_SYMBOL_GPL(regulator_list_voltage);

 /**
+ * regulator_get_hardware_vsel_register - get the HW voltage selector register
+ * @regulator: regulator source
+ * @vsel_reg: voltage selector register, output parameter
+ * @vsel_mask: mask for voltage selector bitfield, output parameter
+ *
+ * Returns the hardware register offset and bitmask used for setting the
+ * regulator voltage. This might be useful when configuring voltage-scaling
+ * hardware or firmware that can make I2C requests behind the kernel's back,
+ * for example.
+ *
+ * On success, the output parameters @vsel_reg and @vsel_mask are filled in
+ * and 0 is returned, otherwise a negative errno is returned.
+ */
+int regulator_get_hardware_vsel_register(struct regulator *regulator,
+					 unsigned *vsel_reg,
+					 unsigned *vsel_mask)
+{
+	struct regulator_dev	*rdev = regulator->rdev;
+	struct regulator_ops	*ops = rdev->desc->ops;
+
+	if (ops->set_voltage_sel != regulator_set_voltage_sel_regmap)
+		return -EOPNOTSUPP;
+
+	 *vsel_reg = rdev->desc->vsel_reg;
+	 *vsel_mask = rdev->desc->vsel_mask;
+
+	 return 0;
+}
+EXPORT_SYMBOL_GPL(regulator_get_hardware_vsel_register);
+
+/**
+ * regulator_list_hardware_vsel - get the HW-specific register value for a selector
+ * @regulator: regulator source
+ * @selector: identify voltage to list
+ *
+ * Converts the selector to a hardware-specific voltage selector that can be
+ * directly written to the regulator registers. The address of the voltage
+ * register can be determined by calling @regulator_get_hardware_vsel_register.
+ *
+ * On error a negative errno is returned.
+ */
+int regulator_list_hardware_vsel(struct regulator *regulator,
+				 unsigned selector)
+{
+	struct regulator_dev	*rdev = regulator->rdev;
+	struct regulator_ops	*ops = rdev->desc->ops;
+
+	if (selector >= rdev->desc->n_voltages)
+		return -EINVAL;
+	if (ops->set_voltage_sel != regulator_set_voltage_sel_regmap)
+		return -EOPNOTSUPP;
+
+	return selector;
+}
+EXPORT_SYMBOL_GPL(regulator_list_hardware_vsel);
+
+/**
  * regulator_get_linear_step - return the voltage step size between VSEL values
  * @regulator: regulator source
  *
diff --git a/include/linux/regulator/consumer.h b/include/linux/regulator/consumer.h
index 14ec18d..fe4cdb2 100644
--- a/include/linux/regulator/consumer.h
+++ b/include/linux/regulator/consumer.h
@@ -215,6 +215,12 @@  int regulator_set_optimum_mode(struct regulator *regulator, int load_uA);

 int regulator_allow_bypass(struct regulator *regulator, bool allow);

+int regulator_get_hardware_vsel_register(struct regulator *regulator,
+					 unsigned *vsel_reg,
+					 unsigned *vsel_mask);
+int regulator_list_hardware_vsel(struct regulator *regulator,
+				 unsigned selector);
+
 /* regulator notifier block */
 int regulator_register_notifier(struct regulator *regulator,
 			      struct notifier_block *nb);